CN102854010B - A kind of engine part fatigue life calculation method based on road state of cyclic operation - Google Patents
A kind of engine part fatigue life calculation method based on road state of cyclic operation Download PDFInfo
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- CN102854010B CN102854010B CN201210382085.5A CN201210382085A CN102854010B CN 102854010 B CN102854010 B CN 102854010B CN 201210382085 A CN201210382085 A CN 201210382085A CN 102854010 B CN102854010 B CN 102854010B
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Abstract
The invention discloses a kind of fatigue life calculation method of the engine part based on road state of cyclic operation, fatigue lifetime corresponding to single cycle impairment value is obtained by single cycle impairment value calculation procedure, circulation milimeter number is obtained by circulation milimeter number calculation procedure, fatigue lifetime corresponding for total for single cycle impairment value is multiplied by circulation milimeter number, namely obtains the fatigue lifetime based on road condition of part; Utilize single cycle impairment value to break wide gap between operating condition of test and real road operating mode, solve engine high-temperature part Calculation of Fatigue Life problem from bottommost layer; The method directly can assess the distance travelled number that part carries car load, specify that product design demand, accelerates the work efficiency of product designer.
Description
Technical field
The present invention relates to a kind of based on road state of cyclic operation engine part fatigue life calculation method.
Background technology
For the Calculation of Fatigue Life of engine high-temperature part (piston, exhaust manifold, cylinder cap etc.), general based on Low Cycle Fatigue Calculation method, i.e. simulated engine bench test operating mode (thermal shock test is carried out to engine high-temperature part), the temperature history of certain part, stress/strain course is calculated under GB (or company standard) operating mode, then single cycle impairment value is calculated according to fatigue damage principle and material behavior, finally according to single cycle computation of Period fatigue lifetime.But the method can only stand life-span (test life) of engine evaluated, can not be applied to the road state of cyclic operation of car load, also namely cannot evaluate this part and be equipped on the mileage number that car load can exercise.At the beginning of designing and developing, lacking a kind of communication bench test and car load road state of cyclic operation, is also the evaluation and computation methods of developer and user.
Summary of the invention
The present invention proposes a kind of engine part fatigue life calculation method based on road state of cyclic operation, solve based in road state of cyclic operation and in bench test, the problem of effectively unified calculation can not be obtained the fatigue lifetime of same engine part.
A kind of fatigue life calculation method of the engine part based on road state of cyclic operation, fatigue lifetime corresponding to single cycle impairment value is obtained by single cycle impairment value calculation procedure, circulation milimeter number is obtained by circulation milimeter number calculation procedure, fatigue lifetime corresponding for total for single cycle impairment value is multiplied by circulation milimeter number, namely obtains the fatigue lifetime based on road condition of part.
The Calculation of Fatigue Life of engine part in described road condition, need first car load road state of cyclic operation to be carried out the reverse engine operating condition calculating correspondence, wherein engine operation condition comprises rotating speed n, engine mean effective pressure P
eand effective engine power P
me;
According to the relational expression of car load and engine
calculate trap for automobile and travel engine speed n corresponding to each moment, wherein, n is engine speed (r/min), u is the car load speed of a motor vehicle (m/s), i
0for base ratio, i
gfor speed changer ratio, r is wheel movement radius (m), and transmission gear ratio is the speed ratio of each gear of variator, and base ratio is the velocity ratio of main reducing gear, speed ratio refers to the ratio of driving and driven bevel gear, i.e. the driven wheel of differential number of teeth/active conical tooth tooth number;
According to car load power balance equation calculation engine power: P
e=P
f+ P
w+ P
j+ P
i, wherein, P
efor engine mean effective pressure, P
ffor tire rolling frictional resistance consumed work, P
wfor air resistance consumed work, P
jfor acceleration resistance consumed work, P
ifor road grade resistance consumed work;
Effective engine power and mean effective pressure are closed and are
wherein, τ is engine strokes number, and V is engine displacement (L).
Described single cycle impairment value calculation procedure is as follows:
Step 1: according to engine operation condition, hydrokinetics calculation is carried out to part working medium and heat eliminating medium, calculate convection transfer rate and fluid temperature (F.T.), hydrokinetics calculation and CFD;
Step 2: map thermal boundary condition, the convection transfer rate obtain the hydrokinetics calculation in step 1 and near wall layer fluid temperature map are to adopting the heat conducting model of FEM (finite element) calculation solid, obtain the boundary condition in solid thermal conduction model, i.e. convection current heat exchange factor and near wall layer fluid temperature;
Step 3: according to the temperature history of the thermal boundary condition calculation engine part obtained in step 2, the temperature history of described part is the temperature process over time of part, and wherein the time is exactly the course of operating condition;
Step 4: according to stress course and the strain history of the temperature history calculation engine part of gained in step 3, consider engine material parameter in computation process, mainly comprise temperature variant linear expansion coefficient, temperature variant Young modulus, Poisson ratio, temperature variant stress-strain diagram, temperature variant viscosity constant, viscous index and viscous strain ratio;
Step 5: according to above-mentioned temperature history, stress course and strain history, utilizes the fatigue properties of material and loop parameter to calculate single cycle impairment value, single cycle impairment value D
iby mechanical damage D
fat, creep impairment D
creepand oxidative damage D
axsummation forms, and wherein the fatigue properties of material are S-N or e-N characteristic, and wherein S-N is S-L, and e-N is strain-life-span, and loop parameter refers to cyclic hardening index, has D
i=D
fat+ D
creep+ D
ax;
Step 6: calculate part life according to impairment value and the relation in life-span:
wherein, N
ffor fatigue lifetime, i.e. cycle index; D
totalfor the total impairment value of single cycle, D
ibe the impairment value of the i-th circulation, n is cycle count.
Described working medium refers to the gas of in-cylinder combustion, comprises the exhaust of exhaust manifold inside, and described heat eliminating medium comprises air for cooling or liquid coolant.
Beneficial effect
A kind of engine part fatigue life calculation method based on road condition of the present invention, by the calculating to engine single road circulation mileage number in car load road state of cyclic operation, corresponding engine operating condition is calculated according to trap for automobile travel situations is reverse, single cycle impairment value is calculated according to engine operating condition and part material, utilize the single road circulation mileage number in car load road state of cyclic operation to be multiplied fatigue lifetime corresponding with single cycle impairment value respectively, obtain the fatigue lifetime based on road condition of part; Utilize single cycle impairment value to break wide gap between operating condition of test and real road operating mode, solve engine high-temperature part Calculation of Fatigue Life problem from bottommost layer; The method directly can assess the distance travelled number that part carries car load, specify that product design demand, accelerates the work efficiency of product designer.
Accompanying drawing explanation
Fig. 1 is process flow diagram of the present invention;
Fig. 2 is road in Europe state of cyclic operation figure;
Fig. 3 is by the engine operating condition of road in Europe state of cyclic operation reverse.
Embodiment
Below with reference to accompanying drawing, the present invention will be further described:
Be illustrated in figure 1 process flow diagram of the present invention, for piston as hot parts, use the present invention to calculate fatigue lifetime to it, comprise car load road cycle life and dynamometer life.
Be illustrated in figure 2 road in Europe state of cyclic operation, can obtain per cycling time in road in Europe state of cyclic operation is 1180 seconds, and often circulation mileage is 11.01Km.
According to road condition calculation engine operating condition, comprise rotating speed n, engine mean effective pressure P
eand effective engine power P
me;
Calculate trap for automobile to travel engine speed corresponding to each moment and be
wherein, n is engine speed (r/min), u is the car load speed of a motor vehicle (m/s), i
0for base ratio, i
gfor speed changer ratio, r is wheel movement radius (m), and transmission gear ratio is the speed ratio of each gear of variator, and base ratio is the velocity ratio of main reducing gear, speed ratio refers to the ratio of driving and driven bevel gear, i.e. the driven wheel of differential number of teeth/active conical tooth tooth number;
According to car load power balance equation calculation engine power: P
e=P
f+ P
w+ P
j+ P
i, wherein, P
efor engine mean effective pressure, P
ffor tire rolling frictional resistance consumed work, P
wfor air resistance consumed work, P
jfor acceleration resistance consumed work, P
ifor road grade resistance consumed work;
Effective engine power and mean effective pressure are closed and are
wherein, τ is engine strokes number, and V is engine displacement (L).
Fig. 3 is by the engine operating condition of road in Europe state of cyclic operation reverse, and rotating speed and effective engine power can obtain from Fig. 3.
Step 2: hydrokinetics calculation is carried out to working medium and heat eliminating medium according to engine operation condition;
According to the engine operation condition by car load reverse, AVL-FIRE software is adopted to carry out hydrokinetics calculation to part working medium (high-temperature exhaust air as exhaust manifold inside) and heat eliminating medium (Flow Field outside as exhaust manifold), wherein the optional software of hydrokinetics calculation is more, as AVL-Fire, Star-CD, Fluent etc.;
Step 3: map thermal boundary condition, adopts ABAQUS software to calculate:
According to the temperature history of the thermal boundary condition calculation engine part obtained in step 2, the temperature history of described part is the temperature process over time of part, and wherein the time is exactly the course of operating condition;
Step 4: according to temperature history calculation engine part stress and the strain history of gained in step 3, need in computation process to consider engine material parameter, mainly comprise temperature variant linear expansion coefficient, temperature variant Young modulus, Poisson ratio, temperature variant stress-strain diagram, temperature variant viscosity constant, viscous index, viscous strain ratio;
Step 5: according to above-mentioned temperature, stress, strain history, utilizes fatigue properties and the loop parameter of material, calculates single cycle impairment value, single cycle impairment value D
i, comprise mechanical damage D
fat, creep impairment D
creepand oxidative damage D
ax, wherein the fatigue properties of material are S-N or e-N characteristic, and namely S-N is S-L, and e-N is strain-life-span, and loop parameter refers to cyclic hardening index, D
i=D
fat+ D
creep+ D
ax;
Step 6: calculate part fatigue lifetime according to impairment value and the relation in life-span:
wherein, N
ffor fatigue lifetime, i.e. cycle index, D
totalfor the total impairment value of single cycle, D
ibe the impairment value of the i-th circulation, n is cycle count.
By calculating, the total impairment value of the single cycle of piston in road in Europe operating mode is 7.34E-5, number so capable of circulation is 1/7.34E-5=13624 time, in road in Europe state of cyclic operation, each circulation distance travelled is 11.01 kilometers, and circulation mileage number is multiplied by single cycle impairment value and obtains this piston car load road life corresponding fatigue lifetime and be: 11.01*13624=15 ten thousand kilometers.
Identical piston carries out bench test, the life-span of carrying out bench test calculates, the total impairment value of single cycle obtained in the bench test of piston is 4.04E-5, number so capable of circulation is 1/4.04E-5=24700 time, 180 seconds each cycling time in national standard test, be multiplied by single cycle impairment value cycling time and obtain this piston stand life-span corresponding fatigue lifetime and be: 0.05*24700=1235 hour;
The bench test fatigue lifetime of engine part and the operating time and the wheeled kilometer that have been calculated part fatigue lifetime by amount of damage of lift-launch car load road state of cyclic operation, this two indices is conducive to deviser to the assurance of design process of parts and user to the operation and maintenance of automobile, make to obtain the fatigue lifetime of engine part and calculate reliably comprehensively, the platform experiment of engine part and obtain effective unification based on the fatigue lifetime of road state of cyclic operation.
Claims (2)
1. the fatigue life calculation method based on the engine part of road state of cyclic operation, it is characterized in that, fatigue lifetime corresponding to single cycle impairment value is obtained by single cycle impairment value calculation procedure, circulation milimeter number is obtained by circulation milimeter number calculation procedure, fatigue lifetime corresponding for total for single cycle impairment value is multiplied by circulation milimeter number, namely obtains the fatigue lifetime based on road condition of part;
Based on the Calculation of Fatigue Life of engine part in road state of cyclic operation, need first car load road state of cyclic operation to be carried out the reverse engine operating condition calculating correspondence, wherein engine operation condition comprises rotating speed n, engine mean effective pressure P
eand effective engine power P
me;
According to the relational expression of car load and engine
calculate trap for automobile and travel engine speed n corresponding to each moment, wherein, n is engine speed r/min, u is car load speed of a motor vehicle m/s, i
0for base ratio, i
gfor speed changer ratio, r is wheel movement radius m, and speed changer is than the speed ratio being each gear of variator, and base ratio is the velocity ratio of main reducing gear, and speed ratio refers to the ratio of driving and driven bevel gear, i.e. the driven wheel of differential number of teeth/active conical tooth tooth number;
According to car load power balance equation calculation engine power: P
e=P
f+ P
w+ P
j+ P
i, wherein, P
efor engine mean effective pressure, P
ffor tire rolling frictional resistance consumed work, P
wfor air resistance consumed work, P
jfor acceleration resistance consumed work, P
ifor road grade resistance consumed work;
Effective engine power and mean effective pressure are closed and are
wherein, τ is engine strokes number, and V is engine displacement L;
Described single cycle impairment value calculation procedure is as follows:
Step 1: according to engine operation condition, hydrokinetics calculation is carried out to part working medium and heat eliminating medium, calculate convection transfer rate and fluid temperature (F.T.), hydrokinetics calculation and CFD;
Step 2: map thermal boundary condition, the convection transfer rate obtain the hydrokinetics calculation in step 1 and near wall layer fluid temperature map are to adopting the heat conducting model of FEM (finite element) calculation solid, obtain the boundary condition in solid thermal conduction model, i.e. convection current heat exchange factor and near wall layer fluid temperature;
Step 3: according to the temperature history of the thermal boundary condition calculation engine part obtained in step 2, the temperature history of described part is the temperature process over time of part, and wherein the time is exactly the course of operating condition;
Step 4: according to stress course and the strain history of the temperature history calculation engine part of gained in step 3, consider engine material parameter in computation process, mainly comprise temperature variant linear expansion coefficient, temperature variant Young modulus, Poisson ratio, temperature variant stress-strain diagram, temperature variant viscosity constant, viscous index and viscous strain ratio;
Step 5: according to above-mentioned temperature history, stress course and strain history, utilizes the fatigue properties of material and loop parameter to calculate single cycle impairment value, single cycle impairment value D
iby mechanical damage D
fat, creep impairment D
creepand oxidative damage D
axsummation forms, and wherein the fatigue properties of material are S-N or e-N characteristic, and wherein S-N is S-L, and e-N is strain-life-span, and loop parameter refers to cyclic hardening index, has D
i=D
fat+ D
creep+ D
ax;
Step 6: calculate part life according to impairment value and the relation in life-span:
wherein, N
ffor fatigue lifetime, i.e. cycle index; D
totalfor the total impairment value of single cycle, D
ibe the impairment value of the i-th circulation, n is cycle count.
2. the fatigue life calculation method of a kind of engine part based on road state of cyclic operation according to claim 1, it is characterized in that, described working medium refers to the gas of in-cylinder combustion, comprises the exhaust of exhaust manifold inside, and described heat eliminating medium comprises air for cooling or liquid coolant.
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| CN104537241B (en) * | 2014-12-30 | 2018-05-11 | 广西科技大学 | Wheel rim flange ring fatigue analysis method |
| CN105466687A (en) * | 2015-12-10 | 2016-04-06 | 浙江国华余姚燃气发电有限责任公司 | A usage life monitoring device used for a high and middle pressure cylinder of a frequently rapid start and stop combined cycle steam turbine |
| CN106802831B (en) * | 2017-01-06 | 2021-02-09 | 无锡威孚力达催化净化器有限责任公司 | Time-averaged temperature field data conversion method for automobile engine post-processing |
| CN108829947A (en) * | 2018-05-30 | 2018-11-16 | 中国电子产品可靠性与环境试验研究所（（工业和信息化部电子第五研究所）（中国赛宝实验室）） | Component reliability evaluation method, device, computer equipment and storage medium |
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| CN110186476A (en) * | 2019-04-11 | 2019-08-30 | 汉腾汽车有限公司 | A kind of algorithm that speedometer for automobile calculates |
| CN113239477B (en) * | 2021-04-01 | 2023-05-02 | 四川大学 | Application of cyclic hardening model based on dislocation entanglement of weld joint in fatigue life prediction of welded joint |
| CN114184405B (en) * | 2021-11-29 | 2023-06-16 | 重庆长安汽车股份有限公司 | Assessment method and system for thermal strain fatigue life of automobile radiator assembly |
| CN114705442B (en) * | 2022-06-06 | 2022-08-19 | 江铃汽车股份有限公司 | Comprehensive fatigue endurance test method for automobile engine |
| CN117928982A (en) * | 2024-03-21 | 2024-04-26 | 合肥松果智造智能科技有限公司 | Experimental platform testing method, operation and maintenance method and storage medium based on road condition information |
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